It is well known to obtain correction of the position of a portion of the spine, or the immobilisation of said portion, by means of vertebral osteosynthesis equipment comprising rigid connecting bars able to connect several vertebrae together, bone anchoring members (hooks or pedicle screws) to obtain anchoring of these connecting bars onto the vertebrae, and connecting parts for rigid connection of the connecting bars to these bone anchoring members.
The treated vertebral portion is frequently the lumbar portion. If it is the lumbar portion of the spine that is treated, the surgeon may wish to anchor the equipment onto the sacrum.
Vertebral osteosynthesis equipments exist which comprise plates to anchor the equipment to the sacrum.
These equipments have the disadvantage however of not always allowing anchoring to the sacrum of high resistance. Much demand is placed on the anchor screws anchored to the first vertebra of the sacrum through movements of the patient, and the cortical bone at this point is of relatively narrow thickness not allowing very strong anchoring. In addition, this bone may be of poor quality.
A further disadvantage of these existing equipments is the fact that the anchoring to the sacrum made possible by these equipments may lead to undesirable major stress being applied to the fifth and fourth lumbar vertebrae.
Various existing equipments are illustrated in the publications of patent applications No EP 1 600 112 A1, U.S. Pat. No. 5,306,275 A and WO 98/55038.